Soda blasting

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A 1965 Rolls Royce after being soda blasted.

Soda blasting is the use of sodium bicarbonate ("baking soda") or sodium bicarbonate-based materials as blast media for paint stripping.

Soda blasting is controversial in hotrodding because substrates that have been soda blasted often display poor adhesion characteristics as a result of blasting residue left on the substrate. In addition, even when the residue is completely removed, soda blasting may offer no savings over conventional media blasting, because of the extra steps required to remove the residue.

Nevertheless, in the right conditions, soda is a useful blasting medium.

Contents

[edit] Soda blasting history

Soda blasting was originally used as a method of stripping/cleaning industrial machinery. It was developed in the 1980's, and was most notably used in the restoration of the Statue of Liberty.

Soda blasting crossed over into the automotive restoration field as somewhat of a miracle process, a misconception that had to be debunked. Although soda has its valid uses as a blast medium, it also has its own set of complexities and nuances that must be taken into consideration.

[edit] Soda blasting procedure

Soda blasting is done with a high volume, low pressure wet or dry blasting machine. Soda cleans surfaces not by abrasion, like conventional blasting media, but by the energy released by the tiny explosion that occurs when the soda particles contact the substrate.

[edit] Soda blasters

details on exactly how soda blasters work, and their various components goes here. could also include a list of manufacturers and possibly details on a DIY home soda blaster

[edit] Soda blasting medium

The sodium bicarbonate used as a blasting medium is chemically identical to "baking soda"; however, the blast medium typically uses larger particles. Some soda blasting media also include additives to prevent caking or help flow, such as tricalcium phosphate or calcium carbonate.

[edit] Examples of soda blasting medium

[edit] Soda blasting residue removal

Removal of residue is crucial to the soda blasting procedure.

Correct soda blasting procedure may involve the following steps after blasting:

  • Cleaning.
  • Blowing dry.
  • Sanding with 180 grit sandpaper.
  • Degreasing.
  • Epoxying.

[edit] Soda blasting residue removal

  • A vinegar and water solution is occasionally recommended, but has also been cautioned against. (needs verification/confirmation)
  • Pressure washer and soap (Simple Green or Purple Power). While the car is wet, rinse with a hose. Do this at least 2-3 times. If any of the residue re-dries, water will not neutralize it, and it will have to be retreated.
  • Dish soap with warm water and a red scuff pad. Scrub panels and rinse with hose three times.

[edit] Resources

[edit] Reasons in favor of using soda blasting

  • Non-destructive, and won't warp panels.
  • Doesn't harm glass, chrome, or rubber (but may harm certain types of plastic trim).
  • Does not cause heat buildup or sparks.
  • Does not abrade or impinge substrate.
  • It's water-soluble, and can typically be washed down a conventional drain.
  • The soda blasting residue can be temporarily left on the substrate, as a rust-inhibiting protective coating.
  • Sodium bicarbonate has a well-known chemistry, and is widely considered safe to use.
  • You can soda blast lightly to leave the body filler intact, and then go over it again to remove all filler.
  • No pre-cleaning required (prior to blasting, traditional blasting media may require the surface to be thoroughly cleaned to remove salt, carbon, or grease).
  • Allows for easier detection of surface flaws. (Traditional abrasive media may peen cracks closed, or fill them with abrasive, whereas soda cleans out the cracks).

For a professional, experienced shop that's well-trained in its use, does all of the finish prep work itself, and has a soda-friendly guarantee from its paint supplier, soda blasting may be a viable choice.

[edit] Reasons against using soda blasting

  • Difficulty of residue removal, especially on parts with cracks/crevices, such as door jambs, engine bays, trunks. Residue can also hide in and behind fasteners.
  • Laborious, time-consuming steps required to prep parts after blasting.
  • Only removes light flash rust.
  • Because soda is so soft, it does not leave an anchor pattern. For reference, see this Mohs hardness scale abrasive comparison chart.
  • Paint manufacturers advise against its use.
  • Can't re-use the medium after blasting.
  • Soda Blasting will not allow for a high silica count paint to adhere to it after process is complete.

Overall, soda blasting is probably not the best choice for the hobbyist or do-it-yourselfer.

[edit] Soda blasting and environmental-friendliness

Soda blasting is frequently touted as an environmentally-friendly blast medium.

However, it's likely no more or less environmentally-friendly than media such as corn cobs, walnut shells, or crushed recycled glass, such as VitroGrit. Aggressively portraying soda blasting as "green" may qualify as green marketing or even borderline greenwashing.

The used soda medium can be screened or filtered, and washed. The water-soluble soda can typically go down a conventional drain, leaving only the blasted particles behind. However, soda blasting medium may contain various flow additives that are less environmentally-friendly.

[edit] Published professional opinions on soda blasting

"NEVER use SPI Epoxy over a Soda Blasted vehicle, Acid Etch/Wash Primer, Rust Converter or other Metal Treatments. NEVER!"

This opinion is expanded upon in this discussion in the Southern Polyurethanes forums.

"We don't recommend sodium bicarbonate, because you can’t clean it out of the pores of the metal well enough."
  • This post contains secondhand email text purportedly from PPG, indicating that PPG does not warranty anything that has been soda blasted. (still waiting on the exact printed warranty text)

[edit] Soda blasting and paint manufacturer warranty voiding

The use of soda blasting is thought to void the warranties of paint manufacturers.

[edit] BASF

BASF does not have a position specific to soda blasting. If this method is used, after all residue is removed, standard substrate preparation procedures must be performed.

[edit] DuPont

Awaiting response.

[edit] Kirker

Reprinted with permission:

Kirker does not encourage the practice of using sodium bicarbonate as a means of preparing a surface for refinish work, especially when we’re talking to the non-professional refinisher, which is probably how the majority of your readers would describe themselves.

Sodium bicarbonate is a very reactive material. Therefore, it is imperative to remove all residue before applying any coating over the blasted surface. Should any trace residue remain on the vehicle (most typically this occurs in seams, along trim molding, etc.), there is a good chance it could react with the coating which results in several product performance issues, the most common being delamination. More specifically, the sodium bicarbonate reacts with acids and/or other materials in the coating, which creates a source for carbon dioxide. As the CO2 gasses out from beneath the forming film, it can cause blisters in the surface which potentially give way to more serious delamination issues.

For removing existing finishes to prepare for refinish work, there are better options than soda including organic media like walnut shells and corn cob or more aggressive abrasives like polyester bead. All of this considered, soda blasting can be done correctly with very good results, however we feel that is outweighed by the extra prep steps required and greater potential for delamination issues.

--Matt Panuska, VP Sales & Marketing for Kirker Automotive Finishes

[edit] PPG

Awaiting clarification and reprint rights.

[edit] Sherwin-Williams

The use of soda blasting does not nullify Sherwin Williams' warranty. However, Sherwin WIlliams discourages its use.

Michael Pellett, a representative from Sherwin-Williams' Dallas Automotive Training Center has stated:

Like most paint companies, we have experienced poor results in the past regarding this process as a surface preparation step. We actively discourage our customers from utilizing this process by explaining the potential problems and offering other alternatives.

For more detail, see the text of the Sherwin Williams warranty.

[edit] Sikkens

Does not recommend Soda Blasting

[edit] SPI

A firsthand response from the owner of SPI is available here.

[edit] Valspar

Does not recommend Soda Blasting.

[edit] Related articles

[edit] References

[edit] External resources

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